Crystal structure studies of natural and synthetic apatites by neutron powder diffraction

A comparison of structural parameters of natural and synthetic apatites from Rietveld refinements of neutron powder diffraction data from room temperature down to 11 K is presented. The natural apatites are a carbonate fluorapatite (francolite) and a fluorapatite (harding pegmatite), while the synthetic sample is a low temperature carbonate hydroxyapatite prepared via hydrolysis of calcium phosphate and sodium bicarbonate. The modification of the structural parameters due to the carbonate substitution show a systematic behavior and they are consistent with the carbonate substitution on the mirror plane of the phosphate tetrahedron.